Methods and arrangements with the features described above are previously known in a number of different embodiments.
For an accurate measurement of the occurrence of a selected gas and/or selected mixture of gases and/or for a careful measurement of the concentration of a gas and/or mixture of gases, there arises a requirement for measurement paths of different lengths, coordinating within the chamber, where one or several such measurement paths are required for a selected gas or mixture of gases, and one or several of the same or different measurement paths is or are required for a second selected gas or mixture of gases.
Thus, the use of a first principle, which will be referred to as Principle (A), is previously known for measurements that require relatively short measurement paths for the associated purpose, related to light reflection of a structure that leads to the concept of wave-guides.
Thus, the use of a second principle, which will be referred to as Principle (B), is also previously known for measurements that require relatively long measurement paths for the associated purpose, related to the use of opposing elliptically shaped mirror surfaces, whereby a light, produced with the form of a point, is allowed to be reflected a number of times between these mirror surfaces, a number of times that has been selected with reference to the desired measurement path, in order in this way to offer an adapted and long measurement path.
It is obvious for one skilled in the arts that even though Principle (B) is intended for an application, according to the pre-conditions specified above, it can also be applied within Principle (A).
The present invention will therefore, for reasons of simplicity, be considered as related principally to Principle (A) described above.
As an example of the prior art, with respect to Principle (A) described above, and of the technical area to which the invention can be considered to be related, the contents of the International Patent document WO 93/11418 (International patent application number PCT/US91/08822) can be mentioned, where FIG. 1 of the said patent publication is also given as FIG. 1 of the present application, for the purposes of illustration, and as an example of technology on which the present invention can be considered to be based.
Here, the use is proposed of a chamber or cell (10), containing a gas sample, adapted such that it can be used for a gas analysis arrangement, that consists of an extended “straight” tube (21) and which has been assigned four, inwardly facing, light-reflecting surfaces (22) assigned to the walls, in order in this way to allow the tube to function as a wave-guide, adapted to lead, not only directly but also following reflection, a somewhat diverging light beam or light cone from a light-emitting means (20) to a detector or light-receiving means (16), with a selected aperture angle and where light rays produced within the light beam are to pass through the contained sample of gas.
In particular, an embodiment is shown here in which a number of penetrating apertures or small holes (24) are applied to the surfaces or the walls of the extended tube (21) and make possible in this manner the slow passage by diffusion of an immediately surrounding gas or mixture of gases into and out from the cell (10).
Particles of smoke and dust, of size greater than 0.1 micrometers, are held outside of the cell (10) by the use of a number of small semi-permeable membranes (28) corresponding in number to the number of apertures, and allowing each one of these to cover one aperture in the tube.
Here is revealed in particular the use of means such that condensation of sample components from the gas can be evaporated by arranging electrical heating of the gas sample that is in the cell to a temperature that lies above the dewpoint temperature of the component that is to be evaluated within the straight tube (21).
In particular, the design is revealed in an embodiment of eighteen (18) diametrically located small holes (24), evenly distributed in four lines along the four sides of the tube and along its complete length, where each hole is provided with one filter. Other embodiments also belong to the prior art, where patent publication U.S. Pat. No. 5,170,064 reveals and describes a gas detector based on infra-red radiation (IR-radiation) that uses a chamber, which has been designed as an elliptical or ellipsoidal reflecting surface.
The ellipsoidal reflecting surface has thus, in a known manner, a first focal point and a second focal point.
One focal point is located within a chamber (4), in order therein to contain an inert gas, and one chamber (3) is adapted to contain the gas sample intended for analysis.
Light-emitting means (24) are here located at one of the focal points (11), and light-receiving means (26) are located at the second focal point (12).
The two chambers or cells (2, 4) are divided from each other by a transparent sheet (15).
Furthermore, the use of detecting means for the selective detection of gases that is previously known is based on optical spectral analysis, such as that which is revealed and described in patent publication U.S. Pat. No. 4,557,603.
Patent publication U.S. Pat. No. 5,973,326 reveals a gas analysis arrangement during the use of a means of emitting infra-red light, located within a chamber, and where the inner surface of this chamber has been assigned properties with high reflectance for light.
In particular, there is revealed here that the light-emitting means is reflected from elliptical or ellipsoidal surfaces and intermediate plane surfaces, in order in this way to be able to focus onto a light-receiving means.
It will be possible also in this case for light radiation formed within the chamber to be absorbed by the gas, contained within the said chamber, in a manner related to frequency, and where a comparison based on frequency between the intensity of the light-emitting means and the intensity related to frequency detected in the light-receiving means creates the conditions required in order to be able to detect not only the occurrence of a gas and/or mixture of gases, but also to measure the current gas concentration.
If the features associated with the present invention and the measures that are required in order to be able to offer rapid reaction times for a gas analysis arrangement of the type described here are considered, then it is true that taking several measures in order to reduce reaction times for the gas analysis are previously known.
Thus it is previously known, in order to increase the sensitivity of a gas analysis arrangement and in order to reduce its reaction time, that it is possible to create the conditions required with the aid of separately driven equipment arranged at the side such that a gas fraction for analysis can be pumped out from a main flow and allowing gas fraction after gas fraction to pass with a selected speed through the chamber that is used for the actual measurement.
It is also previously known to allow the application of the chamber for a gas analysis arrangement in a main flow, whereby the speed of the main flow will determine the reaction time obtained.
The use of various pieces of equipment and means to press a gas or a gas mixture through a chamber within a gas analysis system leads to such systems being denoted as “active” systems.
Gas analysis systems are also known in which the fraction of gas or mixture of gases intended for analysis is allowed, via diffusion, to pass into the chamber. Such a system is denoted as a “passive” system.
With the embodiments of gas analysis arrangements with the features described in the introduction and that as illustrated by the patent publication referred to above, WO 93/11418, it is clear that the small holes formed and distributed along lines in this case will give a very slow diffusion, and that in this way such a gas analysis arrangement will only be able to evaluate delayed, slowly changing average values. The reaction time will, in this way, be very long.
Systems reflecting a light beam also belong to the prior art, as specified in FIG. 8 in the following description, in which the light-emitting means produces a divergent light beam or light cone, and where such a light beam is allowed to reflect from a concave surface, and where the light beam in this way converges towards a receiving means for the light beam, in order to create in this means a strong (intense) image of the light-emitting means.
If the conditions associated with the present invention are considered, it can be seen that for a reflection pattern according to FIG. 8, an undesirable focussed image of the light source is formed at the detector, while the invention aims at being based on the conditions required in order to form an image in the detector of the light source, which, while being in focus, remains diffuse.